Inventory control is frequently maintained by monitoring weight changes in the inventory or by scanning when items are entered in or taken out of the inventory. When the method of monitoring weight changes has been used, it is based on converting weight changes. This technique has been classically done by measuring the total weight of a number of items and dividing the measured weight by the nominal item weight to obtain the number of items. The use of such systems have been limited to situations where the items are nominally uniform in weight, and thus would not be practical for use with inventories which have a number of different item weight classes, such as is typically true of inventories of cigarettes.
For items having different weights, systems have been developed that can identify a single item removed based on a measured weight of the item. U.S. Pat. No. 4,891,755 teaches a system for identifying items removed from a hotel mini-bar by measured change in weight. The '755 patent does not address the possibility of more than one item of any weight class being removed at a time. Another patent which discusses the use of weight to identify a class of item is U.S. Pat. No. 4,512,428, which teaches a weighing apparatus where measured weight is employed to determine whether a roll of coins consists of dimes, nickels, or quarters. The '428 patent apparatus also uses weight to count the number of individual coins in the roll. Again, the invention does not address counting multiple items which may differ in weight.
Weight measurement of a combination of items of differing weights has been employed to assure that a combined weight of items matches an expected weight for the combination. One embodiment taught in U.S. Pat. No. 4,108,363 employs such a scheme for an automated store. Similarly, U.S. Pat. No. 6,384,348 teaches such an approach for verifying that fast food orders have been accurately packed. In both cases, this approach is limited to situations where the expected combination of items to be weighed is known, and the measured weight is simply compared to the expected weight.
Alternatively, a scanning system can be employed to monitor inventory, in which case the items are scanned into and out of inventory. This system requires that the items be coded with a scannable tag such as a bar code. The effectiveness of such a system is dependant on the ability to assure that all items removed or added are scanned into and out of inventory.
Thus, there is a need for a system that can maintain an accurate count of an inventory of items that fall into multiple weight classes while single items or combinations of items are added to or removed from the inventory, as well as a system that can track the time dependence of the changes in inventory and monitor the inventory, which can be helpful in maintaining adequate inventory available and in monitoring for potential theft.